1. Field of the Invention
The present invention relates to a method and equipment for etching a semiconductor device. More specifically, the present invention relates to a method and equipment capable of preventing the side walls of a trench (groove or hole) from being damaged.
2. Description of the Related Art
Recently, silicon (Si) trench etching is applied as a device isolation technique to devices such as in-vehicle pressure-resistant IGBT (insulated gate bipolar transistor) devices corresponding to hybrid vehicles, which is drawing keen attentions in the motor vehicle industry. This method relates to electrically isolating devices by forming a deep trench via dry etching to the device isolation region of the semiconductor device, and embedding an insulating film to the formed trench via CVD (chemical vapor deposition) method or the like.
Moreover, there are active attempts to apply this Si trench to a three-dimensional mount technology, which also requires a deep trench to be formed via etching as described above.
In forming the above-mentioned trench, the depth of the hole (or groove) of the trench profile is required to be as deep as several tens of micrometers, so in order to ensure sufficient throughput, the etching must be performed at high etching rate. Fluoride-based gases having higher reactivity with Si is dominant over chlorine-based gases in the method for realizing high-rate plasma etching.
Japanese Patent Application Laid-Open Publication No. 11-135489 (patent document 1) discloses, for example, a dry etching method carried out by adding approximately 80 to 150 mL/min of HBr (hydrogen bromide) gas to a mixed gas (total flow rate being 24 mL/min) consisting of SF6/O2/SiF4 (sulfur hexafluoride/oxygen/silicon tetrafluoride) to enhance the ion etching performance and to control the trench angle profile to around 90 degrees.
Japanese Patent Application Laid-Open Publication No. 2004-87738 (patent document 2) discloses a dry etching method for processing a trench via a mixed gas plasma using a mixed gas consisting of SF6, O2 and SiF4 to process trenches with an opening diameter or opening width of 3 micrometers or smaller and a depth of 15 micrometers or smaller, or an opening diameter or opening width of 3 micrometers or larger and a depth of 20 micrometers or deeper.
However, according to the above-mentioned prior art performing high-rate etching using mainly fluorine-based gases, the effect of protecting the side walls of the trench is insufficient, and especially when forming a deep trench, the protection of the upper portion of the side walls of the etched trench becomes insufficient while the etching is progressed in the depth direction, causing damages such as recess and roughness to be generated on the surface of the side walls.
That is, considering the embedding process that follows the forming of the trench, the trench must be somewhat tapered, and in that case, the tapered portion of the trench is subjected to damage by the ion bombardment if the ionicity is high. However, there is no consideration on the above problem according to the prior art method disclosed in patent document 1, and since the method carries out etching with high ionicity, the ion bombardment on the inner wall surfaces of the trench may damage the protective layer and generate recesses and surface roughness on the side walls.
Further, according to the prior art method disclosed in patent document 2, there is no disclosure on an etching method related to processing a trench with a small opening (under 3 micrometers) and a deep hole (over 20 micrometers) with a high aspect ratio. Since the etching method for a trench having a high aspect ratio is not established according to patent document 2, the protections on the upper portion of the side walls of the trench having completed etching becomes insufficient, and the side walls are damaged at the end of the etching process.